Apparatus for treating metal sheets



Aug. 3o, 1955 R, v LACKNER 2,716,687

APPARATUS FOR TREATING METAL SHEETS Filed Jan. 29, 195.5Y 2 Sheets-Sheet l Tg1 l 29 l l s lll: 2*

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E BY ROBERT V. LACKNER. M Mvg/w ATTORNEYS Aug. 30, 1955 R. v. LACKNER 2,716,687

APPARATUS EOE TEEATTNG METATJ SHEETS Filed Jan. 29, 1955 2 Sheets-Sheet 2 INVENTOR. ROBERT V. LACKNER.

122% @MAATJE-w ATTORNEYS.

United States Patent O Robert V. Lackner, Pittsburgh, Pa., assigner to Loftus Engineering Corporation, ittsburgh, Pa., a corporation of Maryland Application January 29, 1953, Serial No. 334,001 5 Claims. (Cl. 2191) This invention relates, as indicated, to a method of and apparatus for treating metal sheets, and, more particularly, to improvements for heating the sheet by an electrical resistance heating operation while subjecting it to a stretching and straightening operation.

Metals fabricated in sheet or plate form in many cases must be subjected to a straightening operation before they can be used. A common form of apparatus for this purpose is known as a plate stretcher and .has spaced sets of gripping jaws which engage with the edges of a sheet to be straightened and are moved apart from each other to stretch and thereby straighten the sheet engaged thereby. This type of apparatus has proved satisfactory for most metals such as aluminum, magnesium, stainless steel, and the like which may be worked cold. However, many alloys, particularly alloys high in titanium, are quite tough and resilient at 10W temperatures and are not adaptable to a cold working operation of this character.

This invention has as its principal object the provision in sheet straightening apparatus of the character referred to of improvements for heating the sheet to a temperature at which it will respond to and be worked by tension imparted to its edges. As will become apparent, the improvements of this invention elevate the temperature of the sheet by a resistance heating operation which is eiected by circulating an electrical heating current through the sheet being heated and are directed to the electrical apparatus for elfecting circulation of the heating current through the sheet being treated.

Further objects and advantages of .the invention will become apparent from the following description.

lh`the drawings there is shown a preferred embodiment of the invention. In this showing:

Fig. l is a diagrammatic elevational view of a conventional type 0f apparatus for working metal sheets which is provided with electrical instrumentalities for heating a metal sheet in accordance with the principles of this invention;

Fig. 2 is a plan view of a part of the apparatus shown in Fig. 1 illustrating schematically an electrical circuit for supplying heating current to the sheet being stretched;

Fig. 3 is an enlarged detail fragmentary front elevational view of a pair of gripping jaws used in the apparatus of Fig. 1;

Fig. 4 is an end view looking from the left of Fig. 3;

Fig. 5 is an end view looking from the right of Fig. 3; and

Fig. 6 is a sectional view of an insulating bushing.

In Figs. 1 and 2 of the drawings, the numeral 1 designates a metal sheet to be worked and stretched by the apparatus therein shown. In a manner to be described, the apparatus grips the ends of the sheet and applies an endwise stretching force thereto for the purpose of working and straightening the sheet. Metal sheets worked in this manner usually have a length of from 60 to 144 inches, a width of from about 15 to 72 inches, and a thickness of from about .O15 to .060 inch. As has been indicated above, most metals such as aluminum, stainless steel, magnesium ICC and the like may be worked by this apparatus with the sheets at room temperature, but certain metal alloys, such as the titanium alloys, which are hard and brittle at room temperature are dicult to work in this apparatus..

The apparatus for stretching the sheet 1 comprises a stationary stand or head 2 and a movable stand or head 3 mounted on rollers 4 for movement over a trackway 5 toward and away from the stationary stand 2. The stand 3 is provided with a split clutching nut 6 having threaded engagement with a threaded shaft 7 operated by an electric motor 8 for initially positioning the stand 3 with respect to the stand 2 in accordance with the length of the sheet to be worked. The sheet tensioning and working force is thereafter applied to the stand 3 by an hydraulic motor 9 through a piston rod 10.

The stands 2, 3 are provided with elongated transversely extending openings 11, 12 providing 4pairs of vertically spaced supports 13, 13 and 14, 14. An elongate-operating member 15 of semicircular shape is rotatably secured by suitable mounting structure (not shown) in each of the supports 13, 14. The operating members 15 are arranged in spaced vertical pairs on the supports 13, 14 and are of a length slightly longer than the openings 11, 12 -so that their ends project from the standards 2 and 3 as best shown in Fig. 2. -Each of the operating members 15 has a slot extending over lits entire length in which sheet gripping jaws are mounted, the gripping jaws mounted in the operating members ycarried by the upper supports 13, 14 being designated by the numeral 16, and those mounted in the operating members carried by the lower supports 13, 14 being designated by the numerals 17.

Operation of the apparatus is effected by first actuating the nut 6 to position the stands 2 and 3 so that the ends of the sheet 1 may be arranged between the gripping jaws 16 and 17 as shown in Fig. 1. The nut 6 is then disengaged from the shaft 7, and the vertically spaced pairs of operating members 15 are manually rotated in opposite directions as indicated by the arrows in Fig. 1 to move the jaws 16 and 17 into initial gripping engagement with the ends of the sheet 1. To effect initial manual operation of the jaws 16 and 17 into gripping engagement, one end 0f each vertically spaced pair of operating members 15 is provided with intermeshing gear segments 18, 1S, one of which has a manual operating lever 19 as best shown in Figs. 3 and 5. After initial gripping engagement of the jaws 16 and 17 with the ends of the sheet 1 has been effected in this manner, hydraulic pressure is applied to the cylinder 9 to pull the stand 3 away from the stationary stand 2 and apply tension to the s heet 1. As the tension applied to the sheet 1 increases, the operating members 15 tend to rotate further in the directions indicated by the arrows in Fig. 1 so that the increased tension increases the gripping force of the jaws 16 and 17 with the ends of the sheet. The apparatus thus far described is conventional, and, my present invention consists of certain new and useful improvements of such apparatus.

The structure and mounting of the upper jaws 16, 16 and of the lower jaws 17, 17 are identical and are illustrated by the showing of the single pair in Figs. 3, 4 and 5. In this showing, the rectangular slot extending lengthwise of each of the operating members 15 is designated by the numeral 20 and is provided with a surface covering of insulation 21 which electrically insulates 'the jaws 16 and 17 from the operating members 15 and the stands 2, 3 in which they are mounted. The upper jaw 16 is formed of plural sections 16a each of which is provided with a threaded fastener .22 securing it to its operating member 15. The formation of the upper jaws 16 in sections 16a minimizes warping and provides limited automatic adjustment of their positions with respect to the jaw 17 to insure uniform gripping engagement along the entire length of the sheet.

The lower jaw 17 is continuous and integral from end.

to end so that it may serve as a current distributing electrode in a manner to be described. The lower jaw 17 is preferably provided with at least three fastening members 23, the center one not being shown by reason of the fragmentary showing of Fig. 3, for securing it in position on its operating member 15.

The fastening members 22 and 23 have threaded engagement in openings 24 in the operating members 15 and respectively have enlarged slotted screw heads 25 i receivable in appropriately shaped openings in the clamping jaws secured in position thereby. Each of the jaw openings in which a fastening member 22 or 23 is receivable is provided with an insulating liner 27 of the shape shown in Fig. 6 for electrically insulating it from the jaw held thereby. The liners 21 and 27 thereby operate to completely insulate the jaws 16 and 17 electrically from their operating members 15 and the stands 2 and 3 in which they are mounted. The insulation from which the liners 21 and 27 is constructed is preferably an circuit electrically connected to copper terminal plugs 29 mounted in openings formed in the ends of the lower jaws 17. The transformer 28 is preferably, as indicated, variable for reducing commercially available line current of 110 or 220 volts to a voltage that will result in a current flow suitable for heating the sheet 1. For most metals such as the titanium alloys to be subjected to the heating effect of the circulating current, a reduction of line voltage by the transformer 2S to a value of about l2 to 2O volts will be found satisfactory. While each end of the electrode jaws 17 is shown as having a terminal plug 29 in Figs. 2 and 3, it is to be understood that this is only necessary in the case of the treating sheets having a maximum width and thickness and that uniform distribution in most cases may be had by providing a connection at only one end of each of the electrode jaws 17. ln the event that extremely thick and wide sheets of metal are to be treated, it will be understood further that the distributing plugs 29 may extend axially over the entire length of the electrode jaws 17 to insure uniform current distribution.

From the foregoing, it will be apparent that the clamping jaws 17 Operate to supply a heating current to the sheet in addition to the application thereto of a stretching force. ln the case of titanium sheets, to which this inthrough the sheet between the spaced apart jaws 17, until the temperature of the sheet is raised to from 500 to 700 F., at which temperature the titanium sheet,

' it has been discovered, responds to the tension applied to it and becomes level or flat as desired. The amount of heating required to obtain the essential temperature is of course dependent upon the resistance of the metal, the voltage, and the time in which the current is circulated. The stretching of the sheet by the jaws 16, 17 subjects the sheet to a mechanical stress which is preferably applied simultaneously with the heating operation.

While I have illustrated and described a preferred embodiment of my invention, it will be understood that this is merely by way of illustration, and that various changes and modifications may be made therein within the contemplation of the invention and within the scope of the following claims.

What is claimed is:

l. ln an apparatus for working metal sheets comj prising a pair of stands mounted for movement relative to each other to stretch a metal sheet positioned therebetween and respectively provided with a pair of spaced and elongated operating members mounted for rotation about spaced parallel axes, the invention herein described wherein each of said operating members is provided with a jaw for gripping engagement with an edge of a sheet to be stretched by said stands, at least one of the gripping jaws on each of said pair of operating members being continuous from end to end and constituting an electrode, and an electrical circuit raving terminal connections with said electrodes for circulating a heating current through a sheet engaged by said jaws.

2. ln an apparatus for working metal sheets comprising a pair of stands mounted for movement relative to each other to stretch a metal sheet positioned therebetween and respectively provided with a pair of spaced and elongated operating members mounted for rotation about spaced parallel axes, the invention herein described wherein each of said operating members is provided with :i jaw for gripping engagement with an edge of a sheet to be stretched by said stands, one of said jaws in each of said pairs of operating members being formed of a single integral length of metal and the other being i formed of plural metal segments arranged end to end,

said one jaw constituting a current distributing electrode, and an electrical circuit having terminal connections with said electrodes for circulating a heating current through a sheet engaged by said jaws.

3. ln an apparatus for working metal sheets comprisng a pair of stands mounted for movement relative to fach other to stretch a metal sheet positioned therebetween and respectively provided with a pair of spaced and elongated operating members mounted for rotation about spaced parallel axes, the invention herein described wherein each of said operating members is provided with a jaw for gripping engagement with an edge of a sheet to be stretched by said stands, means mounting and electrically insulating each of said jaws with respect to its operating member, at least one of the gripping jaws on each of said pair of operating members being continuous from end to end and constituting an electrode, and an electrical circuit having terminal connections with said electrodes for circulating a heating current through a sheet engaged by said jaws.

4. ln an apparatus for treating metal sheets comprising a pair of heads mounted for movement relatively to each other, operating members severally mounted for rotary movement in said heads, and means for powerfully i moving said heads to stretch a metal sheet engaged by and between the heads; the invention herein described wherein said operating members are provided with jaws comprising electrodes for securing by clamping engagement the opposite edges of the sheet to be stretched, Ventron is particularly directed, the current 1s circulated means for insulating said jaws from electrical communication with each other except through the intervening body of the engaged sheet, and an electrical circuit having terminal connections with said electrodes for establishing fr a difference in electrical potential between said electrodes and promoting the flow of electrical current in said intervening body of the sheet to heat the sheet to a temperature at which the sheet responds to stretching tension.

5. In an apparatus for flattening titanium sheets, said apparatus comprising a pair of heads mounted for movenient relatively to each other, jaws and jaw-operating members severally mounted for clamping movement in said heads, and means for powerfully moving said heads to stretch a titanium sheet engaged by said jaws; the invention herein described wherein said sheet-securing jaws comprise electrodes for engagement with the opposite edge portions of said sheet, means for insulating said jaws from electrical communication with each other except through the intervening body of the engaged sheet, and an electrical circuit having terminal connections with a 6 said electrodes for establishing a difference in electrical Refeiferaees Cited in the le of this patent potential between said electrodes and promoting the flow UNITED STATES PATENTS of electrical current in the body of the sheet to heat the 1,863,073 Smythe June 14, 1932 2,314,656 Morton Mar. 23, 1943 

